Add role="search" to the global / quicksearch form

Apparently, for accessibility reasons, the search form of a page should be tagged with role="search"
http://wiki.accede-web.com/en/notices/html-css/identifier-les-principales-zones-de-la-page-avec-l-attribut-role?s[]=role&s[]=search

This is done in the form of the Main.Search page, but we should also do it for the global search form , in the menu.